The transcript of a closed-door Nuclear Regulatory Commission meeting two days after the Three Mile Island accident suggests that plant officials discounted early signs of a partial core meltdown - and that such signs have been ignored in a number of other partial meltdowns.
NRC officials said yesterday that all these previous occurrences were either in foreign countries or experimental rather than in commercial U.S. nuclear power plants.
The previous partial meltdowns were referred to by Roger Mattson, NRC director of systems safety, in a taped telephone conversation with NRC Chairman Joseph M. Hendrie as the commission was meeting on the morning of Friday, March 30.
"It is the same way every partial core meltdown has gone." Mattson said of the Three Mile Island sequence. "People haven't believed the instrumentation as they went along. It took us until midnight last night to convince anybody that those goddamn temperature measurements meant something."
These remarks are in transcripts released yesterday by Rep. Morris K. Udall (D-Ariz.), chairman of a House energy subcommittee, who had threatened to subpoena them unless they were turned over.
In his conversation with Chairman Hendrie, Mattson was complaining that Three Mile Island operators at the Metropolitan Edison Co. should have realized earlier than they did that the reactor core had been badly damaged by the accident that began March 28 and that a dangerous hydrogen bubble had been formed inside the reactor located near Harrisburg, Pa.
"We just learned three hours ago that on the afternoon of the first day, there was a 28-pound containment pressure spike that we are guessing may have been a hydrogen explosion," Mattson told Hendrie. "For some reason, they never reported it here until this morning. That would have given us a clue hours ago that we had a partially disassembled core."
Mattson was asked yesterday what he meant by "every partial core meltdown" in the earlier part of his conversation and he first replied that he didn't think he had said "partial core meltdown."
"What that quote means," Mattson said in an interview, "is that there have been incidents where local fuel damage has occurred and in assessing that damage after the fact the literature says that if the operators in command had believed their instrumentation instead of discounting it they'd have done a better job of controlling the accident after it happened."
Later on, Mattson revised his earlier remarks and agreed he had referred to previous partial meltdowns.
"I probably said that," Mattson said in a second interview. "Partial melts have occurred in test reactors and foreign reactors. It happens, you get local melting because of local [coolant] flow blockages."
Mattson emphasized that there had never been an accident as serios as Three Mile Island, where the top third of the reactor core was uncovered and without cooling water for as long as 11 hours and where large amounts of radioactivity were allowed to escape to the air and water.
"This is the first incident that ever damaged this much fuel," Harold C. Denton, director of the NRC's office of nuclear regulation, said in a telephone interview. "I know of no other case where fuel was ever uncovered, overheated like this and so badly damaged." Deliberate Damage
Milton Shaw, former director of nuclear reactors for the NRC predecessor, the Atomic Energy Commission, identified a number of accidents in which fuel damage had taken place. He said there were also a number of deliberate experiments to force fuel damage to see how damaged fuel behaved.
"We destroyed a complete core in 1954 at a test reactor in Idaho Falls," Shaw recalled yesterday. "We've done other destructive test work in Idaho where individual fuel elements were deliberately destroyed."
The partial meltdowns that Mattson meant could have been the partial melt of a single fuel assembly at the Fermi plant of Detroit Edison Co. in 1966, Shaw said. A Canadian reactor suffered fuel damage in 1952 as did a reactor at Hanford, Wash., about the same time.
An experimental reactor in Idaho suffered some core melting in 1955 and a single fuel element at a test reactor in Waltz Mill, Pa., overheated and melted in 1960. In 1958, the core of an experimental reactor in Idaho slumped from a partial melt.
"In all cases, the partial melts came from blockages of coolant to localized parts of the core," Shaw said. "The cores were never uncovered the way Three Mile Island was."
In the NRC transcript released yesterday by Udall, Mattson says Met Ed operators were slow to recognize Three Mile Island's core had been damaged, that a hydrogen bubble had formed which made things worse and that large amounts of radioactivity were in the containment building around the reactor.
"My best guess is that the core uncovered and stayed uncovered for a long period of time and we saw failure modes the likes of which have never been analyzed," Mattson is quoted as saying in the transcript. "Now, we have concluded, some hours ago-I don't know, sometime close after midnight, that we have extensive damage to this core."
Asked later by Commissioner Victor Gilinsky about the extent of damage, Mattson said, "We are estimating now that we probably melted some fuel. We are estimating. I don't know what I would say if a reporter called me and asked me if we melted fuel." 'Horse Race Here'
Mattson went on to say that the operators of the plant were also slow to realize they had a hydrogen bubble forming inside the reactor vessel that possibly was more threatening than the initial damage to the fuel. He went on to tell NRC Chairman Hendrie that the plant operators had tried unsuccessfully a half-dozen times to get rid of the bubble.
"I've got a horse race here," Mattson said. "We've got every systems engineer we can find, except the ones we put on the helicopter, thinking [about] the problem, how the hell do we get the noncondensibles [hydrogen] out of there. Do we win the horse race or do we lose the horse race?"
The NRC said that an analysis of the cooling water at Three Mile Island yesterday showed "insignificant, if any" melting of the fuel had taken place. The NRC added that there had been extensive overheating and damage to the core, short of fuel melt.
Damage takes place as soon as the cladding (coating) around the fuel rods ruptures, usually at about 2,000 degrees. Melting of the uranium fuel does not occur until the core overheats to 5,000 degrees.
"We have less than one-thousandth of 1 percent uranium [in the water sample]," said Victor Stello, director of the division of operating reactors. "It would have to get into whole numbers of 1, 2 percent uranium to be significant in terms of melting."
By late yesterday, technicians had removed from the reactor vessel all of the waste water containing dissolved hydrogen gas. Pressures inside the reactor were pumped down from 1,000 pounds per square inch to 300 pounds per square inch.
The NRC's Denton, said he would like to see pressures rise to 400 pounds so the big pumps that operate at those pressures can take over and complete the final task of bringing Three Mile Island to "cold shutdown" where the water coolant temperature drops to below the boiling point. Final shutdown could take place sometime this weekend.
The NRC ordered the operators of other pressurized water reactors to take note of the possibility that a hydrogen bubble might form in their reactors as it did at Three Mile Island. In a bulletin to the 34 plants in the United Stats, the NRC warned that the hydrogen bubble might not be unique to the Pennsylvania plant in the case of a similar chain of events.
"Prepare and implement all changes necessary" to seal off the reactor building to keep radioactivity from escaping to the atmosphere as it did at Three Mile Island, the bulletin said.
It ordered operators to take note of more than one instrument before making decisions and to leave automatic systems running when they start until there is careful review of plant conditions. Operators trusting a misleading pressurizer gauge and overriding emergency pumps at Three Mile Island were among "apparent operational errors which led to the eventual core damage," the order said. Improving Safety
In the future, the directive continued, operators must "assure very early notification of serious events." NRC members complained in the transcript and at congressional hearings this week that they had had major problems in obtaining early and accurate information on events at Three Mile Island.
Earlier yesterday Carl Walske, president of the Atomic Industrial Forum, the nuclear trade association, said the industry's faith in nuclear power was "basically unshaken" by the Pennsylvania accident. "Nuclear power would have been dead a long time ago if it weren't for all the problems other energy generating forms are having," he noted.
The industry's main concerns, he said at a breakfast with reporters, are eliminating the human errors involved in Three Mile Island and the threat of huge financial losses in the wake of any accident. Walske proposed that some type of risk-sharing fund or commitment be organized among the nuclear-owning utilities in order to spread the costs of any accident around the country.
Nuclear power safety "can be improved . . . After Three Mile Island and its lessons are absorbed, our reactors will be safer than they were," Walske continued. "There will always be some risk, but compared with the other ways of doing the same job - oil, coal, dams or whatever-the risks of nuclear will still be small."
South Carolina, which was unwilling to allow trucks bearing waste from Three Mile Island to enter the state, was informed yesterday by the NRC that the trucks were back in Harrisburg. "We asked them to futher confirm what's in this waste and that's what they're going to do," said Heyward G. Shealy, director of the state's Department of Health and Environmental Control.
American Nuclear Insurers, the firm that provides liability insurance to most nuclear plants, said yesterday it has paid out a total of $939,000 to persons who evacuated the area around Three Mile Island. Property claims have not yet been processed, including those for damage to the reactor. Walske said he thought that damage would be less than the $300 million for which Metropolitan Edison is insured. CAPTION: Picture 1, JOSEPH M. HENDRIE . . . a dearth of information; Picture2, Portion of transcript of systems safety director Roger Mattson speaking on telephone to NRC meeting.